I think the excitement around this is partially people overestimating the properties of this particular material, but also partially people excited that if this is true, the method by which it works might result in the discovery of materials with even better properties.

Even this paper doesn't claim to have a particularly good superconductor as far as overall performance is concerned. It's not particularly close to the state of the art in critical field or current. But if it does turn out that their hypothesis claiming that the internal stress of the material allows it to bypass the current need for extremely high pressures / low temperatures, then perhaps there can be new materials developed that are better superconductors while still overcoming the current limitations presented by REBCOs and other leading superconductors. Also, that's not even mentioning that LK-99 has no particularly exotic materials. REBCOs rely on rare earth elements like Yttrium, but this just uses lead, copper, and phosphorus.